Workshop participants
SPC:
- Claudio Castillo-Jordán
NOAA PIFSC:
- Rob Ahrens
- Felipe Carvalho
- Nicholas Ducharme-Barth
- Michelle Sculley
Pre-workshop status
- 2024 assessment used MULTIFAN-CL (MFCL) framework
- Cubic splines defined selectivity as function of age
- Limited by 10 annual age classes
- Constraints on selectivity curve shape
- SPC developed quarterly age model (
mfcl-1979-20p3)- Improved selectivity resolution
- Created mismatch with striped marlin reproductive biology
Key challenge
Quarterly vs Annual Population Dynamics
- Striped marlin have restricted spawning season (late austral spring/early summer)
- MFCL quarterly model introduced year-round recruitment
- Need for modeling approach that could:
- Provide finer resolution for selectivity
- Maintain annual population dynamics aligned with biology
Workshop approach
- Shift from MULTIFAN-CL to Stock Synthesis
- Investigate key issues
- Poor fits to size and index data
- Data conflicts
- Model initial conditions
- Growth curve
Advantages of Stock Synthesis:
- Can model selectivity as function of length
- Maintains annual population dynamics
Model development process
Stepwise development:
- Base Stock Synthesis model (1979 start):
01-mls-base-1979
- Refined selectivity & data treatment:
03-chg-selex-1979
- Reverted to 1952 start year:
04-start-1952
- Excluded problematic size data:
06-exclude-more-comp
- Added catch uncertainty:
07-catch-uncertainty
- Refined growth modeling:
12-CAAL-old-growth-SD
Key changes
Initial conditions:
- Returned to 1952 start year with unfished state
- Better addressed population initialization concerns
- Consistency with
diagnostic-2019
Key changes
Selectivity:
- Length-based selectivity provided greater resolution
- Double-normal functional form with estimated parameters
- Further refinements needed (beyond range of observations)
Key changes
Size data exclusion:
- Excluded problematic size composition data:
- Mixed-fleet data with temporal patchiness
- Fleets with small sample sizes
- Data showing internal conflicts
- Data with quality concerns
- Generally improved fit to remaining data components
Key changes
Growth:
- Internal estimation using conditional age-at-length data
- Addressed some limitations from externally derived growth curve
- Improved overall model fit
- Growth slower but still struggles fitting smallest observations
Key changes
Catch uncertainty:
- Implemented catch uncertainty for early high-catch periods
- Bifurcated Japanese LL fleet in sub-region 2
- Reduced sensitivity to potentially unreliable historical catch
Additional investigation
- Investigated source of misfit to the index seen in 2000 - 2002
- Ran additional models to remove the influence of:
- the index highpoint in 1998 (
16-CAAL-rm-spike) - Fleet 6 (Australian LL; sub-region 2) weight frequency data (
17-CAAL-noAU-ASPM)
- the index highpoint in 1998 (
- Conflict is driven by the Fleet 6 weight data which suggests an increasing trend
Remaining challenges
- Spatiotemporal heterogeneity in fleet coverage
- No single fleet samples all areas consistently
- Different spatial coverage during different time periods
- Potential non-representativeness in mixed-fleet size data
- Limitations in age data from opportunistic sampling
- Longline will select for fastest growing younger individuals
- Data weighting remains challenging
